Magnetic tape cassette, tape reel and magnetic tape

ABSTRACT

A tape reel ( 10 ) is so constructed that an upper flange ( 12 ) and a lower flange ( 13 ) are respectively provided at an upper and a lower ends of a cylindrical reel hub ( 11 ) around which a magnetic tape ( 20 ) is wound, and a maximum value of a distance from the upper flange ( 12 ) and the lower flange ( 13 ) to lateral ends of the magnetic tape ( 20 ) is set to be 0.5 mm or more, and less than 1.0 mm. The magnetic tape ( 20 ) includes a nonmagnetic substrate ( 21 ), a magnetic layer ( 22 ) provided on one face of the nonmagnetic substrate and a back layer ( 23 ) provided on the other face of the nonmagnetic substrate, and in a state where the magnetic tape is wound around the tape reel ( 10 ), a distance (U 1 +D 1 ) from the upper flange ( 12 ) and the lower flange ( 13 ) to lateral ends of the back layer ( 23 ) is larger than a distance (U 2 +D 2 ) from the upper flange ( 12 ) and the lower flange ( 13 ) to lateral ends of the nonmagnetic substrate ( 21 ) or lateral ends of the magnetic layer ( 22 ). Further, a magnetic tape cassette is provided with at least one of the above described tape reel ( 10 ) and the magnetic tape ( 20 ). Owing to the above described structure, it is possible to provide the tape reel, the magnetic tape and the magnetic tape cassette in which dropout and output variation are restrained and irregular winding can be prevented.

TECHNICAL FIELD

The present invention relates to a tape reel and a magnetic tape whichare applied to a magnetic tape cassette, and more particularly to thetape reel provided with an upper and a lower flanges at an upper and alower end of a reel hub, and the magnetic tape to be wound around thetape reel.

BACKGROUND OF THE INVENTION

Conventionally, there have been various types of magnetic tapecassettes, namely, for a video recorder, audio apparatus, computer, etc.For example, there has been a type of the magnetic tape cassette for thevideo recorder which includes a cassette case consisting of an upper anda lower cassette half and a pair of tape reels having a reel hub and anupper and a lower flange rotatably contained in the cassette case in astate where a magnetic tape is wound around the reel hub.

FIG. 5 shows a basic structure of the above described tape reel. Asshown in the drawing, a tape reel 110 includes a reel hub 111 aroundwhich a magnetic tape 120 is wound, an upper flange 112 fixed to anupper end of the reel hub 111, and a disc-like lower flange 113integrally formed at a lower end of the reel hub 111. In this example, alower face of the upper flange 112 is tapered with respect to a planeperpendicular to an axial direction of the reel hub 111 in such a mannerthat a radially outer side of the lower face is inclined upward in thedrawing. An upper face of the lower flange 113 is tapered in such amanner that a radially outer side of the upper face is inclined downwardin the drawing.

Recently, in order to record enormous amounts of information data in asmall space, according to digitalization and downsizing of magneticrecording apparatuses, an intention is to improve recording density. Themagnetic tape has been made thinner for improvement of volumetricrecording density, and tracks have been made narrower for improvement ofplanar recording density.

Recently, in order to record enormous amounts of information data in asmall space, according to digitalization and downsizing of magneticrecording apparatuses, it is intended to improve recording density. Themagnetic tape has been made thinner for improvement of volumetricrecording density, and tracks have been made narrower for improvement ofplanar recording density.

However, because the magnetic tape has been made thinner, the magnetictape has become likely to be deformed in a lateral direction. Forexample, there have been some cases in which the magnetic tape hasdeformed in a lateral direction during fast feeding or at accelerationor deceleration of the tape in a recording and reproducing apparatus,and has locally got in touch with a guide roller and so on intensively,resulting in occurrence of a curve or a weaving of the magnetic tape. Inaddition, there has been a tendency that due to the deformation of themagnetic tape, the lateral ends of the magnetic tape may get in touchwith the lower face of the upper flange or the upper face of the lowerflange to generate abrasion powder, and dropouts may be increased.

Meanwhile, as the tracks of the magnetic tape have been made narrower, aso-called linearity defect is likely to happen such that reproducingoutput in the deformed area of the tape may become lower thanreproducing output in a rectilinear area. Therefore, even a minutedeformation of the tape may result in the linearity defect. As a result,the aforesaid weaving of the magnetic tape will incur and increase thelinearity defect, in other words, there will be a variation of thereproducing output.

Moreover, because the magnetic tape has become narrower, so-calledirregular winding may occur in some cases, when the magnetic tape hasbeen wound around the reel hub. Also, and as shown in FIG. 6, which isan enlarged perspective view of a part A of FIG. 5, a part of the end ofthe magnetic tape may jump out from a plane formed by the ends of themagnetic tape 120. As shown in FIG. 6, the part 120 a of the end of themagnetic tape that jumps out will be deformed weavingly like sea weed.In the case where the magnetic tape has deformed like sea weed, normalrecording and reproduction cannot be expected. Therefore, it isextremely important to prevent such irregular winding.

Although various factors have been considered as causes of the irregularwinding, it is considered that one cause is air that may enter betweenadjacent magnetic tapes when the magnetic tape 120 is wound around thereel hub 111 of the tape reel 110, and the magnetic tape may be pushedupward while the air escapes. In the case of a conventional magnetictape having a thickness of about 10 μm for example, the irregularwinding has been able to be restrained by providing a groove in the reelhub 11 of the tape reel. It is considered that because the tape had alarge thickness and relatively high rigidity, the magnetic tape couldhave been wound without involving air by such a measure.

However, as the magnetic tape has become thinner and thinner, it hasbecome more and more difficult to restrain the irregular winding, eventhough the groove has been provided in the reel hub. It has been foundthat the irregular winding is likely to happen especially in a casewhere the thickness of the tape is 7 μm or less.

Meanwhile, it has been found that almost all of the abrasion powderoccurring when the ends of the magnetic tape get in touch with the lowerface of the upper flange and the upper face of the lower flange ispowder generated through abrasion of a back layer. As shown in FIG. 6,the magnetic tape 120 has been heretofore in a shape of parallelogram incross section. A magnetic recording medium having a large width willinevitably take such a shape when it has been cut by means of a rotarycutter to form the magnetic tape 120. Accordingly, a large amount of theabrasion powder is generated from a part B where an end of the backlayer has projected from ends of a magnetic layer and a nonmagneticlayer in a lateral direction of the magnetic tape.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above describedproblems, and its object is to provide a magnetic tape cassette, a tapereel and a magnetic tape in which output variation or dropout can berestrained, and which can perform more accurate recording andreproduction. Particularly, an object of a first embodiment of theinvention is to provide the tape reel around which the magnetic tape canbe smoothly wound, in which occurrence of deformation in a lateraldirection of the magnetic tape and irregular winding can be restrained,and which can perform more accurate recording and reproduction. Further,an object of a second embodiment of the invention is to provide themagnetic tape in which an amount of abrasion powder occurring when theends of the magnetic tape get in touch with the lower face of the upperflange and the upper face of the lower flange is decreased, and whichcan perform more accurate recording and reproduction.

The inventors of this invention have had an intensive study and foundthat deformation of the magnetic tape in a lateral direction andirregular winding can be remarkably restrained by decreasing a distancebetween the upper flange and the lower flange in the tape reel into adetermined distance. Conventionally, it has been considered that if thedistance between the upper flange and the lower flange has beendecreased, the magnetic tape would be unable to be smoothly wound aroundthe tape reel. However, by setting this distance between the upperflange and the lower flange to be the determined distance taking a widthof the magnetic tape into consideration, the magnetic tape can besmoothly wound around the tape reel, and the deformation of the magnetictape in a lateral direction and occurrence of the irregular winding canbe restrained.

Specifically, the first aspect of the present invention is a tape reelcomprising an upper flange and a lower flange respectively provided atan upper end and a lower end of a cylindrical reel hub around which amagnetic tape is wound, characterized in that a maximum value of adistance from the upper flange and the lower flange to lateral ends ofthe magnetic tape is 0.5 mm or more, and less than 1.0 mm.

Moreover, in a case where a thickness of the magnetic tape is 6 μm ormore, and less than 11 μm, the deformation of the magnetic tape in alateral direction and occurrence of the irregular winding can be morereliably restrained.

On this occasion, in a case where the lower face of the upper flange andthe upper face of the lower flange are respectively tapered, a distancefrom the ends of the outermost magnetic tape which has been wound aroundthe tape reel to the lower face of the upper flange and the upper faceof the lower flange will become “a maximum value of the distance fromthe upper flange and the lower flange to the lateral ends of theaforesaid magnetic tape”. In a case where the lower face of the upperflange and the upper face of the lower flange are in parallel to eachother, the distance from the upper flange and the lower flange to thelateral ends of the aforesaid magnetic tape is constant.

Further, the inventors have found as a result of their intensive studythat the occurrence of abrasion powder can be remarkably decreased by aconstruction where an end of the back layer does not project from an endof a nonmagnetic layer in a lateral direction of the magnetic tape.

Specifically, the second aspect of the present invention is a magnetictape comprising a nonmagnetic substrate, a magnetic layer provided onone face of the nonmagnetic substrate and a back layer provided on theother face of the nonmagnetic substrate, the magnetic tape being adaptedto be wound around a tape reel having an upper flange and a lower flangerespectively provided at an upper end and a lower end of a cylindricalreel hub, characterized in that in a state where the magnetic tape iswound around the tape reel, a distance from the upper flange and thelower flange to lateral ends of the back layer is larger than a distancefrom the upper flange and the lower flange to lateral ends of thenonmagnetic substrate or lateral ends of the magnetic layer.

Further, the distance from the upper flange and the lower flange to thelateral ends of the back layer may be larger than both the distance fromthe upper flange and the lower flange to the lateral ends of thenonmagnetic substrate and to the lateral ends of the magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of a part of an embodiment accordingto the invention;

FIG. 2 is a partial sectional view of a part of another embodimentaccording to the invention;

FIG. 3 is a plan view showing a general structure of a magnetic tapecassette to which a magnetic tape and a tape reel in the embodimentsaccording to the invention can be applied;

FIG. 4 is a sectional view of a part showing a structure of the magnetictape cassette;

FIG. 5 is a view showing a conventional tape reel; and

FIG. 6 is a view showing the magnetic tape which has been wound in aconventional manner.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a tape reel 10 and a magnetic tape 20 according to anembodiment of the invention. The tape reel 10 includes a reel hub 11 ina cylindrical shape around which the magnetic tape 20 is wound, an upperflange 12 in a disc-like shape fixed to an upper end of the reel hub 11,and a lower flange 13 in a disc-like shape formed at a lower end of thereel hub 11 integrally therewith. In this embodiment, a lower face ofthe upper flange 12 is tapered with respect to a plane perpendicular toan axial direction of the reel hub 11 in such a manner that a radiallyoutward side is inclined upward in the drawing, and an upper face of thelower flange 13 is tapered in such a manner that a radially outward sideis inclined downward in the drawing.

The magnetic tape 20 is wound around the reel hub 11 of the tape reel 10so that gaps are respectively created between the lower face of theupper flange 12 and one of lateral ends of the magnetic tape 20 (anupper end in the drawing), and between the upper face of the lowerflange 13 and the other lateral end of the magnetic tape 20 (a lower endin the drawing).

In this embodiment, a width W1 of the magnetic tape 20 is 12.65 mm, anda thickness is 10 μm. On this occasion, a distance W2 between the lowerface of the upper flange 12 and the upper face of the lower flange 13 ata position of an outermost magnetic tape which has been wound around thereel hub 11 in a radial direction of the upper and lower flanges 12, 13is set to be between 13.15 mm or more and 13.65 mm or less.

In the magnetic tape 20, as shown in a part encircled by an alternatelong and short dash line in FIG. 1, a lateral end of a back layer 23does not project from lateral ends of a magnetic layer 22 and anonmagnetic layer 21 in a lateral direction of the magnetic tape 20. Inother words, a distance from the upper and lower flanges 12, 13 to theends of the back layer 23 (a sum of a distance U1 between the lower faceof the upper flange 12 and an upper end in the drawing of the back layer23, and a distance D1 between the upper face of the lower flange 13 anda lower end in the drawing of the back layer 23) is larger than adistance from the upper and lower flanges 12, 13 to the ends of themagnetic layer 22 (a sum of a distance U2 between the lower face of theupper flange 12 and an upper end in the drawing of the magnetic layer22, and a distance D2 between the upper face of the lower flange 13 anda lower end in the drawing of the magnetic layer 22).

The magnetic tape 20 having such a sectional shape can be formed byadjusting delivery speed of a magnetic recording medium and peripheralspeed of a rotary cutter when the magnetic recording medium having alarge width is cut by the rotary cutter.

According to the tape reel 10 and the magnetic tape 20 having the abovedescribed structure, deformation of the magnetic tape 20 in the lateraldirection when the magnetic tape 20 is wound around the reel hub 11 isrestricted by the lower face of the upper flange 12 and the upper faceof the lower flange 13 which are spaced at a determined interval.Moreover, since the lateral end of the back layer will not get in touchwith the lower flange 13, abrasion powder will not be generated from theback layer 23. Therefore, linearity defects and dropouts can be reliablydecreased.

FIG. 2 shows a tape reel 30 in another embodiment according to theinvention. Those members which have been already described will bedenoted by the same reference numerals or corresponding signs in thedrawing, and their description will be simplified or omitted.

In this tape reel 30 too, a lower face of an upper flange 32 is taperedin such a manner that a radially outward side is inclined upward in thedrawing, and an upper face of a lower flange 33 is tapered in such amanner that a radially outward side is inclined downward in the drawing.A magnetic tape 40 is wound around the tape reel 30 so that one oflateral ends (a lower end in the drawing) of the magnetic tape 40 may bein contact with the upper face of the lower flange 33.

In this embodiment, a width W1 of the magnetic tape 40 is 6.35±0.3 mm, athickness is 6.7+0/−0.4 μm (In other words, the thickness has atolerance of 0 in a plus direction and a tolerance of at most 0.4 in aminus direction from a standard of 6.7 μm). In this case, an amount ofinclination T1 of the upper flange 32 is 0-0.15 mm, an amount ofinclination T2 of the lower flange 33 is 0.25-0.5 mm, a height of a reelhub 31, that is, a distance T3 between the lower face of the upperflange 32 as and the upper face of the lower flange 33 near the reel hub31 is 6.75 mm. A diameter of both the upper and lower flanges 32, 33 maybe about 60 mm, and an outer diameter of the reel hub 31 may be about 19mm.

It is to be noted that the amount of inclination T1 of the upper flange32 in this embodiment means a height of an outer circumferential end Q1of the upper flange 32 provided that a height of a root P1 of the reelhub 31 is zero, in case where the lower face of the upper flange 32 istapered in such a manner that the radially outward side is inclinedupward in the drawing. Similarly, the amount of inclination T2 of thelower flange 33 in this embodiment means a height of an outercircumferential end Q2 of the lower flange 33 provided that a height ofa root P2 of the reel hub 31 is zero, in a case where the upper face ofthe lower flange 33 is tapered in such a manner that the radiallyoutward side is inclined downward in the drawing.

On occasion when winding the magnetic tape 40 around the tape reel 30,in a case where the magnetic tape 40 a to be wound may be deformed in alateral direction and get in touch with the lower face of the upperflange 32 as shown in FIG. 2, the relevant magnetic tape 40 a will bepushed by the lower face of the upper flange toward the lower flangewithout generating abrasion powder. Then, the relevant magnetic tape 40a will get in touch with the upper face of the lower flange 33 when itis abutted against the outermost magnetic tape 40 which has been alreadywound.

On occasion when successively winding the magnetic tape around the tapereel 30, while a distance between the upper end in the drawing of theoutermost magnetic tape which has been already wound and the lower faceof the upper flange 32 is 1 mm or less, the magnetic tape 40 a will bepushed toward the lower flange by the above described action, andreliably get in touch with the upper face of the lower flange 33. Withthis action, occurrence of the irregular winding can be remarkablyrestrained.

EXAMPLES

Now, remarkable effects of the invention will be described referring toexamples of the invention.

Tape reels having such a shape as shown in FIG. 1 and having such flangewidths as shown in Table 1 (Examples 1 to 3, Comparative examples 1 to4) are constructed employing magnetic tapes having such tape thicknessesand tape widths as shown in Table 1. Then, magnetic tape cassettes havebeen produced employing these tape reels. Variation of outputs andincrease of dropouts (DO) of the produced magnetic tape cassettes havebeen measured. The results of the measurements are shown in Table 1.

For reference, the variation of the outputs has been measured. It is 0%in a case where a width of an envelope of an RF output is normal and itis 100% in a case where there is no signal. The increase of the dropoutshas been measured by running the magnetic tapes 300 times of FF/REWusing a video tape recorder and by counting a number of dropouts per0.2μsec. or more before and after the running.

TABLE 1 Tape (U2 + D2) thick- Tape Flange − Output Dropout ness widthwidth (U1 + D1) Varia- increase (μm) W1 (mm) W2 (mm) (μm) tion (%)(No./μsec) Ex. 1 10.8 12.65 13.55 −0.3 20 100 Ex. 2 10.2 12.65 13.20−0.1 10 230 Ex. 3 6.5 6.35 7.25 −0.2 35 170 Com- 10.6 12.65 14.00 −0.265 120 para- tive Ex. 1 Com- 10.4 12.65 13.50 +0.2 20 2500 para- tiveEx. 2 Com- 6.3 6.35 7.60 −0.4 80 110 para- tive Ex. 3 Com- 6.6 6.35 7.20+0.1 40 1800 para- tive Ex. 4

As apparent from Table 1, the variation of the outputs was low in themagnetic tape cassettes employing the tape reels in which a maximumvalue of the distance from the upper and lower flanges to the ends ofthe magnetic tape is 0.5 mm or more, and less than 1.0 mm. Moreover, theincrease of the dropouts has been remarkably restrained in the magnetictape cassettes employing the tape reels in which the distance from theupper and lower flanges to the ends of the back layer is larger than thedistance from the upper and lower flanges to the ends of the nonmagneticsupport and to the ends of the magnetic layer.

Next, material for molding the tape reels which are suitable for theembodiments of the invention and other embodiments will be described.

The upper flange 32 of the tape reel 30 is preferably formed oftransparent resin from a viewpoint of confirming a remaining amount ofthe tape. The lower flange 33 integrally provided with the reel hub 31around which the magnetic tape 20 is wound is preferably constructed bymolding synthetic resin as described below.

(1) POM (polyacetal) resin molded in consideration of slidingperformance (wear resistance),

(2) PS (polystyrene) added with Si (silicone) and resin molded inconsideration of cost performance,

(3) ABS (acrylonitrile-butadiene-styrene) resin, ABS resin added with PC(polycarbonate), PC resin or PC resin added with glass fiber forreinforcement in consideration of strength, and so on.

However, the inventors have found as a result of the intensive studythat there may still exist a concern, in the lower flange of the tapereel in the embodiments of the invention and other embodiments, that thelower flange may be abutted against an edge of an opening of a lowercassette half and scrape each other to generate abrasion powder. Also, adropout of a signal due to adhesion of the abrasion powder to themagnetic tape may happen, such that there is still room for furtherimprovement. Measures for the improvement which the inventors have foundwill be explained hereunder.

In the magnetic tape cassette 30 employing the tape reel 10 and themagnetic tape 20 according to the embodiments of the invention and theother embodiments, when an upper cassette half 82 is removed, a pair ofthe tape reels 30 (one of the tape reels is omitted in the drawing) arerotatably mounted in a lower cassette half 83 as shown in FIG. 3.

In a structure as shown in cross section in FIG. 4, the lower flange 33is held in a state where its center part is engaged in an opening 91formed in the lower cassette half 83, and a part of the lower flange 33is mounted on an edge (projecting frame) 91 a of the opening 91.

In a case where the magnetic tape cassette 80 is mounted on a videoapparatus to conduct recording and reproduction, as the pair of the tapereels 32 rotate to run the magnetic tape 20, the pair of the tape reels30 are raised floatingly and the lower flange 33 will not get in touchwith the edge 91 a. However, during transportation as a product, thereis a risk that they may get in touch with each other as shown in thedrawing and scrape each other, resulting in occurrence of abrasionpowder.

Therefore, as a measure for improvement, the lower flange 33 includingthe reel hub 31 composing the pair of the tape reels 10 has been moldedfrom the following resin material.

Specifically, the lower flange 33 was molded of resin material of ABSresin containing 0.2 to 1.2% of a compound of phosphate ester,preferably ethylene-bis-phosphate of phosphate ester.

The ABS resin has been selected for reasons such as strength,dimensional stability, production cost, prevention of dimensional changein an ambient temperature at 80° C. during transportation, etc., andethylene-bis-phosphate of phosphate ester has been selected as anadditive having vibration suitability, that is, good slidingperformance, and heat resistance. Further, a ratio of adding theadditive has been calculated from an experiment, for preventingcontamination of molds by the additive.

Result of the experiment: In a case where the content ofethylene-bis-phosphate of phosphate ester is smaller than 0.2%, it isnot effective with respect to the aforesaid vibration suitability or so,and in a case where the content is larger than 1.2%, contamination ofthe molds during continuous molding may occur.

The ABS resin has been selected for reasons such as strength,dimensional stability, production cost, prevention of dimensional changein the ambient temperature at 80° C. during transportation, etc., andthe compound of phosphate ester, preferably ethylene-bis-phosphate hasbeen selected as the additive having vibration suitability and heatresistance. Further, the ratio of adding the additive has beencalculated from the experiment, for preventing contamination of themolds when molding.

Accordingly, the mold will not be soiled when the tape reels arecontinuously molded, and productivity can be enhanced. In addition,because the strength and vibration suitability are improved, abrasionpowder will not occur due to abrasion during transportation of theproducts and production steps, and the problems of dropouts of signalsdue to adhesion of the powder to the magnetic tape, fractures, chips,etc. can be prevented.

Furthermore, effects such as the tape reel having excellent dimensionalstability, is free from deformation due to the ambient temperatureduring transportation, and the production cost not rising, and so on canbe obtained.

INDUSTRIAL APPLICABILITY

As described herein above, the tape reel according to the invention hasa maximum value of 0.5 mm or more and less than 1.0 mm of the distancefrom the upper and lower flanges to the lateral ends of the magnetictape. Accordingly, variation of outputs and dropouts can be remarkablyrestrained and irregular winding can be reliably prevented.

In the magnetic tape according to the invention, the distance from theupper and lower flanges to the ends of the back layer is larger than thedistance from the upper and lower flanges to the ends of the nonmagneticsupport or to the ends of the magnetic layer. Accordingly, the dropoutscan be more remarkably restrained.

Further, the magnetic tape cassette provided with at least one of theabove described tape reels and the above described magnetic tape canconduct more accurate recording and reproduction, remarkably restrainingthe variation of the outputs and the dropouts.

What is claimed is:
 1. A tape reel comprising an upper flange and alower flange respectively provided at an upper end and a lower end of acylindrical reel hub around which a magnetic tape is wound, saidmagnetic tape having a width of 6.32 mm to 12.65 mm, wherein a maximumvalue of a sum of a distance from said upper flange to an upper lateralend of said magnetic tape and a distance from said lower flange to alower lateral end of said magnetic tape is 0.5 mm or more, and less than1.0 mm, and wherein said lower flange is molded of synthetic resinincluding ABS resin mainly containing a compound of phosphate ester. 2.The tape real as claimed in claim 1, wherein said compound of phosphateester is contained in an amount of 0.2 to 1.2%.
 3. A magnetic tapecassette comprising a magnetic tape, and a tape reel having an upperflange and a lower flange respectively provided at an upper end and alower end of a cylindrical reel hub around which said magnetic tape iswound, said magnetic tape having a width of 6.32 mm to 12.65 mm, whereina maximum value of a sum of a distance from said upper flange to anupper lateral end of said magnetic tape and a distance from said lowerflange to a lower lateral end of said magnetic tape is 0.5 mm or more,and less than 1.0 mm, and wherein said lower flange is molded ofsynthetic resin including ABS resin mainly containing a compound ofphosphate ester.
 4. The magnetic tape cassette as claimed in claim 3,wherein said compound of phosphate ester is contained in an amount of0.2 to 1.2%.
 5. The magnetic tape cassette as claimed in claim 3,wherein said magnetic tape includes a nonmagnetic substrate, a magneticlayer provided on one face of said nonmagnetic substrate and a backlayer provided on the other face of said nonmagnetic substrate, and in astate where said magnetic tape is wound around said tape reel, adistance from said upper flange and said lower flange to lateral ends ofsaid back layer is larger than a distance from said upper flange andsaid lower flange to lateral ends of said nonmagnetic substrate or tolateral ends of said magnetic layer.
 6. The magnetic tape cassette asclaimed in claim 5, wherein in said state where said magnetic tape iswound around said tape reel, said distance from said upper flange andsaid lower flange to said lateral ends of said back layer is larger thanboth said distance from said upper flange and said lower flange to saidlateral ends of said nonmagnectic substrate and said distance from saidupper flange and said lower flange to said lateral ends of said magneticlayer.
 7. The magnetic tape cassette as claimed in claim 3, wherein athickness of said magnetic tape is 6 μm or more and, less than 11 μm.